1. Field of the Invention
The present invention relates to heatsinks and more particularly to a heatsink including an embedded heat pipe for thermally managing a high power CPU in a desktop computer.
2. Description of the Relevant Art
A computer system typically includes, at a minimum, an input/output (I/O) port, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and a signal bus. Desktop computers and other similar workstations, typically include a printed circuit board (or xe2x80x9cmotherboardxe2x80x9d) to which the CPU, memory components (such as ROM and RAM integrated circuits), I/O control, and discrete components such as resistors and capacitors are affixed and selectively interconnected via conductive traces within the printed circuit board. The power dissipated by a typical CPU generates large amounts of thermal energy. Advances in CPU speed and bus throughput have further compounded this problem.
Conventional desktop computers are typically thermally managed by forcing ambient air across the motherboard and particularly across the CPU through the use of a fan placed upon the minicomputer chassis and, in some instances, an additional fan placed directly above the CPU. In lieu of or in addition to a fan, many desktop manufacturers further employ a conventional heatsink upon the CPU. A heatsink is generally made of metal having opposed surfaces, wherein one surface is mostly flat while the other surface includes a plurality of outward-extending fins. The flat surface is thermally bonded to the encapsulated CPU, allowing the fins to project into the ambient air within the desktop chassis. A silicon compound is often used as the thermal bonding agent. The metal fins function similar to a metal radiator in that they remove heat from the thermally bonded, underlying CPU by means of conduction, convection and radiation.
CPUs and other integrated circuits designed for desktop applications are typically required to operate within a specified temperature range. Industry custom is to specify the xe2x80x9ccase temperaturexe2x80x9d operating range for a given integrated circuit. The case temperature (TC), for purposes of this disclosure, refers to the temperature at the top center of the integrated circuit package. The case temperature is related to the junction temperature TJ and the ambient temperature TA as follows:
TJ+TC+(P*"THgr"JC)xe2x80x83xe2x80x83Eq.1
TA=TJxe2x88x92(P*"THgr"JA)xe2x80x83xe2x80x83Eq.2
where:
TA=ambient temperature (xc2x0 C.)
TJ=average junction temperature (xc2x0 C.)
TC=case temperature at top center of package (xc2x0 C.)
P=power dissipated by the integrated circuit (W)
"THgr"JC=junction-to-case thermal resistance (xc2x0 C./W)
"THgr"JA=junction-to-ambient thermal resistance (xc2x0 C./W)
combing Eq. 1 and Eq. 2 and rearranging yields:
TC=TA+P*"THgr"CAxe2x80x83xe2x80x83Eq.3
where "THgr"CA=("THgr"JAxe2x88x92"THgr"JC)
Equation 3 reveals that an increase in power P results in an increase in the case temperature TC as well unless steps are taken to reduce the ambient temperature TA, reduce the case-to-ambient thermal resistance "THgr"CA, or both. In most environments in which desktop computers are operated, the consideration of human comfort and the cost of air conditioning place a minimum temperature beyond which reducing the ambient temperature is unfeasible. To remain within the operating specifications of a high power CPU, it is therefore typically necessary to reduce the thermal resistance.
In many applications, conventional heatsinks as described above provide a cost effective mechanism for dissipating heat and thereby effectively reducing the thermal resistance of the integrated circuit. With the advent of high power CPUs (i.e., CPUs that consume greater than approximately 40 Watts), conventional heatsink design is typically unable to adequately dissipate the generated heat. A need therefore exists for a thermal management system within a high power CPU desktop computer which is both cost effective and operably superior to conventional heatsinks.
The problems identified above are in large part addressed by a heatsink for dissipating thermal energy generated by a microprocessor. The heatsink includes a thermally conductive base, a plurality of conductive fins, and a heat pipe contained within the base. The heat pipe distributes heat generated by a concentrated heat source such as the CPU to the peripheral portions of the heatsink for more efficient thermal management.
Broadly speaking, the present invention contemplates a heatsink for dissipating thermal energy generated by a microprocessor and neighboring peripheral components. The heatsink is affixed to a printed circuit board within a computer housing. The heatsink includes a thermally conductive base, a plurality of thermally conductive fins, and a heat pipe. The thermally conductive base includes substantially planar upper and lower surfaces displaced from each other by a thickness of the base. The base defines a first channel, proximal to the lower surface, extending from a first end of the base to a second end. The plurality of conductive fins extends substantially perpendicularly from the upper surface of the base. Each of the plurality of fins includes substantially planar proximal and distal major surfaces displaced from each other by a thickness of the fins. The heat pipe is contained within the first channel of the base. The heat pipe includes an elongated casing containing a heat transfer medium and a wick. The wick is immersed in the medium extending along a major access of the heat pipe. The heatsink is configured to be affixed to the printed circuit board with the heat pipe aligned over the center of the microprocessor and the lower surface of the heatsink in close proximity with an upper surface of the microprocessor.
The thermally conductive base, in a presently preferred embodiment, is comprised of aluminum, copper, silver, tungsten or any appropriate alloy thereof. In one embodiment, the base is substantially rectangular and has a thickness in the range of approximately 2 to 20 mm. A length of the base in a presently preferred embodiment is in the range of approximately 100 to 155 mm. The width of the base is preferably in the range of approximately 50 to 100 mm. Each of the plurality of thermally conductive fins is similarly sized and each of the major surfaces is substantially rectangular. In one presently preferred embodiment, the plurality of fins are arranged upon the base upper surface in an array comprised of a plurality of rows and columns. In one embodiment, the major surfaces of the fins are oriented perpendicular to a direction of the columns. Each of the fins extends to a height above the upper surface that is greater than a gap between adjacent rows by a factor in the range of approximately 10 to 20. The height of the fins in a preferred embodiment is in the range of approximately 30 to 40 mm and the gap between adjacent rows is preferably in the range of approximately 1.5 to 4.0 mm.
In a preferred embodiment, the plurality of fins and the conductive base are fabricated from a continuous piece of material such that the fins are integrally formed with and connected to the conductive base. The heat pipe casing in a preferred embodiment is made of copper or aluminum. A cross-section of the heat pipe casing in a first embodiment is substantially rectangular. In this embodiment the first channel preferably comprises a rectangularly shaped trench formed into the lower surface of the conductive base. In an alternative embodiment, the heat pipe casing is substantially circular in cross-section and the first channel is a circular tunnel suitably drilled or extruded into the conductive base proximal to the lower surface. The heat pipe fluid is ideally water, acetone, methanol, or ethanol. The conductive base may further include a second channel where the second channel extends substantially perpendicularly to the first channel. In this embodiment, the heatsink ideally further includes a second heat pipe contained within the second channel. The conductive base, in one embodiment, may still further include first and second diagonal channels. The diagonal channels suitably extend between respective corners of the base. In such an embodiment, the heatsink further includes first and second diagonal heat pipes contained within the first and second diagonal channels respectively.
The present invention further contemplates a motherboard for use in a computing system. The motherboard includes a printed circuit board, a central processing unit, a random access memory device, and a heatsink. The central processing unit is affixed to the printed circuit board. The random access memory is affixed to the circuit board and interfaced to the central processing unit. The heatsink is a heatsink according to the heatsink of the present invention. The heatsink is affixed to the printed circuit board with the heat pipe aligned over a center of the microprocessor. The lower surface of the heatsink is in close proximity with an upper surface of the microprocessor.